Methods for forming ceramic powders into complex shapes are desirable in many areas of technology. For example, such methods are required for producing advanced, high-temperature structural parts such as heat engine components, recuperators and the like from ceramic powders. Generally, two methods are presently known for forming ceramic powders into complex or intricately shaped parts. Specifically, one method comprises machining a green blank to the desired shape. However, this method has significant drawbacks in that the machining is time consuming, expensive, and in a practical sense, inapplicable to some complex or varied cross-sectional shapes, for example, turbine rotors. A second method for forming ceramic powders into complex or intricatley shaped parts comprises injection molding a composition which comprises the ceramic powder and a polymeric and/or wax-like binder as a vehicle for the ceramic powder.
For example, the Strivens U.S. Pat. No. 2,939,199 discloses a method of forming articles from ceramic powders wherein the ceramic powders are mixed with a vehicle comprising a thermosetting material and a plasticizer, and the resultant mixture is injection molded into a mold of a desired shape and heated to cure the thermosetting component. The vehicle is then removed from the molded part by low pressure distillation or by solvent extraction. A similar method is disclosed in the Kingery et al U.S. Pat. No. 3,351,688 wherein the ceramic powder is mixed with a binder such as paraffin at a temperature where the binder is liquid, and the resulting mixture is cast into a mold of the desired shape. The binder is permitted to solidify so that a green piece is formed having a uniform density. Use of a paraffin wax binder for molding ceramic powders into desired shapes is also disclosed in the Curry U.S. Pat. No. 4,011,291 and the Ohnsorg U.S. Pat. No. 4,144,207. The Rivers U.S. Pat. No. 4,113,480 and the Wiech, Jr. U.S. Pat. No. 4,197,118 disclose additional methods for molding parts from metal powders by mixing the powders with binder materials and injection molding the resultant mixtures. Additional methods of interest which employ binder materials are also disclosed in the Huther et al U.S. Pat. No. 4,478,790 and the Kato U.S. Pat. No. 4,460,527.
The aforementioned injection molding techniques using various binder materials also have significant drawbacks. Generally, the binder removal times are unacceptably long, being up to a week or more in some instances, and binder removal often creates cracks or warpage in the molded parts. Additionally, after binder removal, the strength of the molded parts is relatively low whereby increased breakage of the parts occurs during subsequent handling. It is also difficult to provide molded parts having a large cross section, for example, parts greater than one inch in cross section, or having widely varying cross sections, that is, with both thick and thin regions, using the injection molding techniques.
Thus, the presently known methods for forming complex and intricately shaped parts from ceramic powders are disadvantageous in various respects. Moreover, a need exists for a method for molding ceramic powders into complex and intricately shaped parts, which method overcomes the disadvantages of the known techniques.